This invention relates generally to improvements in fluid filters, and more particularly to a relief valve for a motor vehicle oil filter.
A spin-on, throw-away type of fluid filter is now commonly used as an oil filter for motor vehicles because it is relatively inexpensive to mass produce and easy to install and replace. Presently, research and development regarding throwaway filters is directed to producing the filters less expensively, while maintaining or improving the filter's efficiency.
A spin-on, throw-away filter usually has, among other things, a filter housing with an open end covered partially by a mounting plate having a plurality of pores to allow oil to flow from the motor to the inside of the filter and a threaded central aperture for connecting the filter to the motor and transmitting oil from the inside of the filter back to the motor, a closed or domed end, a cylindrical filter element extending substantially from the open end to the closed end and being spring biased toward the open end but being spaced a certain distance from the open end, a centertube extending longitudinally at the interior of the filter element, and a relief valve having "open" and "closed" positions and being located between the open end and the filter element.
Under normal operating conditions, oil flows from the motor, through the mounting plate pores, through the filter element, through the closed relief valve, out the threaded central aperture and back to the motor.
Under abnormal operating conditions, i.e., when the filter element reaches its maximum dirt holding capacity or high pressure surges are experienced, such as cold starts of the motor, the relief valve is caused to open and immediately returns oil to the motor to assure sufficient oil reaches motor parts requiring lubrication, thus by-passing the filter element altogether.
Basically, two types of fluid filter relief valves are known in the art. The first type is the "tension spring housing" type and the second type is the "capturing legs" type. Each of these types of relief valve will now be generally described.
The tension spring housing type of relief valve usually comprises an outlet neck or member abutting the inside of the mounting plate of the filter and extending to adjacent the filter element, a cup-shaped tension spring housing which normally functions as the relief valve oil inlet member and which is fixedly connected to and extending from the outlet neck toward the closed end of the filter and into the filter element, and a spring-biased, relatively flat piston therebetween. The outlet neck functions as the sealing surface for the piston.
Examples of prior art tension spring housing type relief valves for fluid filters include:
______________________________________ U.S. PAT. NO. INVENTOR ISSUED ______________________________________ 3,061,101 HUMBERT, JR. 10/30/62 3,146,194 HATHAWAY 8/25/64 3,187,896 WILKINSON 6/8/65 3,315,809 HULTGREN 4/25/67 3,473,664 HULTGREN 10/21/69 3,618,775 HULTGREN 11/9/71 3,633,750 BRAUN ET AL. 1/11/72 3,640,390 GOY ET AL. 2/8/72 3,724,665 HALL 4/3/73 ______________________________________
In the tension spring housing type, both the tension spring housing and the outlet neck are usually "deep drawn". Deep drawing is a relatively expensive manufacturing method for forming large depth/diameter ratios in sheet or strip metal by considerable plastic distortion in dies. In practice, cupshaped, box-shaped or cone-shaped articles or shells are produced by forcing a drawable metal into a punch press or drop hammer. From a manufacturing cost standpoint, it is desirous to hold drawn members to a minimum depth or to use as few deep drawn members as possible.
The outlet neck is deep drawn because it is necessary to keep the filter element in spaced relation to the mounting plate for proper operation of the filter. The inlet member is deep drawn in order to house the coil spring.
The deep drawn outlet neck of the tension spring housing type relief valve functions as a relatively flat sealing surface for receiving the piston in sealing relation. This design results in several drawbacks from a valve efficiency and manufacturing cost standpoint. More specifically, when the filter is assembled, a vertical force is created in the direction of the mounting plate by a spring at the dome end of the filter assembly which urges the filter element toward the open end of the filter. Of course, the filter element transfers this force through the relief valve upon which it rests. The deep drawn outlet neck is eventually required to support this vertical force. Since the flat sealing surface of the outlet neck is positioned perpendicular to this vertical force, any deformation of the outlet neck caused by the vertical force, e.g., bending or collapsing of its walls, results in the sealing surface becoming non-parallel to the relatively flat piston and leakage occurs through the relief valve at pressures far below the pressure required to open the valve. In effect, the relief valve by-passes oil at times when all of the oil should be flowing through the filter element.
Due to the possibility that the outlet neck will collapse or bend under the vertical force, it is necessary to manufacture the outlet neck from a material whose thickness can withstand the vertical force after assembly and thus keep the flat sealing surface parallel to the piston, i.e., perpendicular to the vertical force. Of course, a design requiring a thicker metal for the outlet neck will increase manufacturing costs, and attempting to deep draw this thicker metal will also increase costs.
Further, the tension spring relief valve of the prior art uses a soft rubber piston to seal against the sealing surface of the outlet neck. Restricting an oil filter design solely to soft rubber may also increase manufacturing costs. In addition, it is generally known that a flat, soft rubber piston resting against a flat sealing surface does not offer a dependable seal when used in an oil filter.
In summary, the above-discussed tension spring housing relief valve demands expensive manufacturing because deep drawing is more costly than holding drawn parts to a minimum depth or using as few deep drawn parts as possible. In addition, deep drawn outlet necks usually use a flat sealing surface which may cause leakage if the outlet neck collapses under pressure.
The second type of relief valve, i.e., the capturing legs type, usually uses a long molded nylon valve having at one end a plurality of hooked legs for capturing and holding a spring and at the other end a deeply formed outlet neck. Like the tension spring housing type, the oil outlet neck or member of the capturing legs type is positioned at the open end of the filter and is deeply formed in order to properly space the filter element from the mounting plate. The capturing legs extend toward the closed end and are necessarily long in order to receive and hold the coil spring. Finally, the capturing legs relief valve comprises a relatively flat piston between the spring and outlet neck for sealing the relief valve while in the closed position.
Examples of prior art capturing legs type relief valves for fluid filters include:
______________________________________ U.S. PAT. NO. INVENTOR ISSUED ______________________________________ 3,156,259 HAVELKA ET AL. 11/10/64 3,589,517 PALMAI 6/29/71 4,028,243 OFFER ET AL. 6/7/77 ______________________________________
The outlet neck of the capturing legs type of relief valve also functions as the sealing surface for the piston, as does the outlet neck of the tension spring housing type relief valve. Again, this design has several drawbacks from a valve efficiency and manufacturing cost standpoint. More specifically, when a filter using a capturing legs type relief valve is assembled, a vertical force is still created in the direction of the mounting plate by a spring at the dome end of the filter assembly, which urges the filter element toward the open end of the filter. Of course, the filter element transfers the vertical force through the relief valve. The outlet neck is eventually required to support this vertical force. Since the relatively flat sealing surface of the outlet neck is positioned perpendicular to the vertical force, any loss of structural integrity under the vertical force results in the sealing surface becoming non-parallel to the piston and leakage occurs through the relief valve at pressures far below the pressure required to open the valve. In effect, the relief valve passes oil at times when all of the oil should be flowing through the filter element.
Since today's engines are made smaller to do the same amount of work that larger engines did a decade or more ago, these smaller engines run at higher temperatures. The molded nylon valve used in, for example, the Havelka U.S. Pat. No. 3,156,259 may, if the temperature of the oil exceeds the softening point of the nylon, lose its structural integrity causing the sealing surface to become non-parallel to the piston under the force mentioned and causing leakage around the piston.
In addition, as is similar to the tension spring housing type relief valve, the capturing legs type relief valve requires a soft rubber piston to seal against the relatively flat sealing surface of the outlet neck. Again, restricting the oil filter design to a particulr type of rubber may increase overall costs and a flat, soft rubber piston does not provide an adequate seal against a relatively flat sealing surface (although the Havelka U.S. Pat. No. 3,156,259 indicates the use of a metal piston, this patent in practice also requires a molded rubber piston with a standard metal piston support to effect the desired seal, as is evidenced by the U.S. Pat No. 3,589,517 and Offer et al. U.S. Pat No. 4,028,243, which utilize the basic design of the relief valve of the Havelka et al. U.S. Pat. No. 3,156,259 along with a rubber piston).
Finally, regarding the capturing legs type of relief valve, e.g., the Havelka et al. U.S. Pat. No. 3,156,259, a molded nylon valve costs far more than the electroplate tin or steel used to make the deep drawn tension spring housings and outlet necks.
Thus, in regard to the capturing legs type of relief valve, the use of a molded nylon member creates manufacturing costs higher than a relief valve employing electroplate tin or steel. In addition, if the temperature of the oil exceeds the softening point of the nylon, the capturing leg member can lose its structural integrity and can cause unwanted leakage through the relief valve.
In summary, each of the two prior art types of relief valve uses a deep outlet neck for spacing the filter element from the mounting plate and for functioning as the sealing surface for the piston, each uses a deep drawn or long inlet member for holding the coil spring, each uses a spring urging the piston against the outlet neck, and each is susceptable to structural deterioration under the vertical force exerted upon the relief valve once the filter is assembled.
Overall, it is desirous that a relief valve be capable of the lowest cost manufacture and be capable of efficient sealing properties. For example, a design which allows for use of a relatively shallow drawn, thin electroplate material has a cost advantage over a design which uses a deep drawn thick steel or molded nylon. In addition, having flexibility in choosing the piston materials and structural design thereof is preferred to being limited to a particular type and configuration of rubber. Finally, it is desirous that a valve be capable of relatively quick and easy automated assembly and require no welding, brazing, or soldering in assembly.
Thus, it can be seen that known prior art oil filter relief valves for spin-on, throw-away type oil filters continue to have manufacturing drawbacks. None of the known prior art devices have the novel features of the invention disclosed herein for eliminating such manufacturing drawbacks.